Mass Effect
- Modify the classes so they have more clearly defined strengths and weaknesses. Also, adept is taken down a notch.
- Less planets to explore, more variety and nuance to compensate.
- Less weapon models all-around, more variety to compensate.
- Consolidate the various scavenger quests (League of One, Matriarch Dilinaga, etc.) into actual missions.
- Probably some changes to the main missions. I'm not sure, it's been a very long time since I've played the first game.
Mass Effect 2
- The Council doesn't outright reject you. After running through various psych tests and whatnot, they ask you to find decisive proof of the Reaper invasion rather than assuming Pascal's Mugging from a crazy dude.
- Going from #1, a dual storyline emerges. Help Cerberus stop the Collectors, find proof of the Reaper invasion, and navigate the middle ground when those two goals clash. Have consequences, non-moral ones, for when you pursue one at the expense of another.
- Through your old connections, you have access to other organizations to assist you. They won't do the dirty work, but they'll provide you with relevant information and ask for favors in return.
- Cerberus doesn't blatantly announce its arrival every time you dock the Normandy or bring a Cerberus member i.e. no visual identification.
- People aren't magically aware of the movements of a supposedly clandestine organization (Cerberus).
- NPCs wear armor in appropriate circumstances.
- More content relating to the ME universe in loyalty missions. Some missions had strong tie-ins, others sadly did not. You know which ones I'm talking about.
- People don't recognize Shepard on sight. She is a legend, but mostly in name and reputation.
- Either leave planet scanning and introduce a galactic market system so excess mining can be rewarded, or drop it in favor of another in-game economy system.
- Bring back the option to buy better omni-tools if the galactic market exists. Have it pass on to ME3.
- Bring back certain ammos from ME1 (Sledgehammer, Toxic).
- Modified reputation system based on Alpha Protocol. Instead of Paragon/Regenade, you have to read the personalities of NPCs and their ability to spread information. The former determines how individual NPCs react to you, the latter dictates the perception of the larger galactic community and the future responses of individual NPCs.
- Cut out the foreshadowing of Space Jesus Shepard. Emphasis other aspects that allow Shepard to accomplish these missions and be an exemplar of humanity.
Mass Effect 3
- Carry over ME2 changes to ME3.
- Better pacing, Since ME2 will ideally let the galactic races prepare for the invasion (to the extent they buy into it), the storyline won't have to crush all its various strands into such a short period.
- Better weapon and armor customization.
- Pseudo-AP rep system carries over.
- Your former teammates' influence on the storyline is affected by your influence on them. Not completing loyalty missions, but the overall attitudes and actions you conveyed to them during their stay on the Normandy. Some will positively take on "Paragon" traits, others react better to "Renegade" ones.
- No "geth are secretly pining to be like us" ending. A lot of people will disagree, but I was disappointed how the writers went Hollywood at the last minute. When dealing with emergent AI, Hollywood generally goes for Skynet or Pinocchio. The geth were interesting because they defied such simplistic dichotomies.
- Bring back a little of the sociopathic ME1 Wrex in certain scenarios.
- Rachni have a larger part to play.
- Reapers are the main enemy. Cerberus is still overall a rational organization who helps you in useful, and perhaps misguided, ways. TIM doesn't go full idiot for the sake of plot.
- Bring back some, not all, of ME2's squadmates. They overall had more interesting personalities and things to contribute than ME3 squadmates. This is just my opinion.
- Don't know how to resolve the last act.